1. Technical Field Disclosure
The disclosure relates to a varactor, and more particularly, to a varactor with a through-wafer via (TWV) structure.
2. Description of the Related Art
Three-dimensional (3D) integrated circuits and stacked chips or wafers are used to solve some development limitations of two-dimensional integrated circuits. Typically, a three-dimensional integrated circuit is formed by using through-wafer vias (TWVs) in a semiconductor substrate, to provide the stacked chip/wafer packaging structures, such as using the through-wafer vias to connect the chips or wafers. Therefore, the lengths of the metal wires and the impedances of the wires/traces are decreased and the chip area is also reduced, thereby having the advantages: small size, high integration, high efficiency, low power consumption and low cost.
Before making a three-dimensional stack, different chips or wafers are separately completed by the suitable front-end processes (such as the processes for forming active devices, connecting the metal lines and so on), and then the through-wafer vias and the re-distributed layers (RDLs) are used to complete the stack steps of the back-end processes, wherein the process step is also known as a via last process. Nowadays, the back-end processes are further used to form various integrated passive devices (IPDs), so as to efficiently use the back-end process areas. Furthermore, the passive devices of the front-end processes can be implemented by the back-end processes, and the passive devices can be connected by the through-wafer vias, so as to decrease the expensive front-end process areas, thereby reducing manufacturing costs. At present, the varactors are often used in high-speed circuits. However, the production of the varactor requires a plurality of masks and process steps.
Therefore, a varactor with a through-wafer via structure is desired.